EP3611034A1

EP3611034A1 - Elastomer-metal cord composite and tire using same

Info

Publication number: EP3611034A1
Application number: EP18784349.5A
Authority: EP
Inventors: Kazuki Uemura
Original assignee: Bridgestone Corp
Current assignee: Bridgestone Corp
Priority date: 2017-04-11
Filing date: 2018-04-09
Publication date: 2020-02-19
Anticipated expiration: 2038-04-09
Also published as: WO2018190309A1; EP3611034B1; EP3611034A4; JPWO2018190309A1; US20200039294A1; CN110494301A

Abstract

Provided are: an elastomer-metal cord composite capable of improving the performance of a tire, in which composite a metal cord composed of a bundle of metal filaments that are parallelly aligned without being twisted together is coated with an elastomer; and a tire including the same. An elastomer-metal cord composite (10) is obtained by coating, with an elastomer (3), a metal cord (2) composed of a bundle of two to ten metal filaments (1) that are parallelly aligned in a single row without being twisted together. The metal filaments (1) are patterned in the same patterning amount at the same pitch, and the metal cord (2) includes at least one pair of adjacent metal filaments (1) having different phases from each other.

Description

TECHNICAL FIELD

The present invention relates to an elastomer-metal cord composite and a tire. More particularly, the present invention relates to: an elastomer-metal cord composite obtained by coating, with an elastomer, a metal cord composed of a bundle of metal filaments that are parallelly aligned without being twisted together; and a tire including the same.

BACKGROUND ART

In recent years, there is an increasing demand for weight reduction of tires for the purpose improving the fuel efficiency of automobiles. As means for reducing the tire weight, metal cords for belt reinforcement have been drawing attention, and a large number of techniques for using metal filaments as a belt cord without twisting have been disclosed. For example, Patent Document 1 proposes a tire in which, for improvement of lightweightness and durability, a belt layer is constituted by at least two belt plies each obtained by arranging metal filament bundles along the width direction in a coating rubber, the metal filament bundles being formed by parallelly aligning small-diameter metal filaments at a high tensile strength without twisting. In this tire, the number of the metal filaments in each metal filament bundle is optimized in accordance with the metal filament diameter. Further, it is also proposed to adjust the thickness of the metal filament bundles in the radial direction to have a specific ratio with respect to the thickness of the belt plies.

RELATED ART DOCUMENT

PATENT DOCUMENT

[Patent Document 1] JP2001-334810A

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

However, in Patent Document 1, although the lightweightness and the durability were examined, no examination was made on other performance. Therefore, in the use of metal filaments as a belt cord without twisting, there is expected to be a demand for further improvement as the tire performance is improved in the future.
In view of the above, an object of the present invention is to provide: an elastomer-metal cord composite capable of improving the performance of a tire, in which composite a metal cord composed of a bundle of metal filaments that are parallelly aligned without being twisted together is coated with an elastomer; and a tire including the same.

MEANS FOR SOLVING THE PROBLEMS

The present inventor intensively studied to solve the above-described problems and obtained the following findings as a result. That is, the use of a metal cord obtained by bundling metal filaments without twisting them together suppresses in-plane deformation of the metal cord when a compressive input is made to a belt treat, and this leads to deterioration of the fatigue characteristics of the metal cord. In addition, in a metal cord obtained by bundling metal filaments without twisting them together, a rubber hardly infiltrates between adjacent metal filaments, and this causes the generation of a non-rubber-coated region where metal filaments are not coated with the rubber. Accordingly, the metal filaments are displaced from each other during tire rolling and, due to the resulting reduction in the in-plane rigidity, the steering stability may be impaired. Based on these findings, the present inventor further intensively studied and consequently discovered that the above-described problems can be solved by adopting the following constitution for a bundle of metal filaments, thereby completing the present invention.
That is, an elastomer-metal cord composite of the present invention is obtained by coating, with an elastomer, a metal cord composed of a bundle of two to ten metal filaments that are parallelly aligned in a single row without being twisted together, the elastomer-metal cord composite being characterized in that:
the metal filaments are patterned in the same patterning amount at the same pitch, and the metal cord includes at least one pair of adjacent metal filaments having different phases from each other.
FIG. 1 is a drawing of a metal filament that describes the definitions of a patterning amount (h) and a patterning pitch (p) of the metal filament, and the "patterning amount (h)" refers to the width of undulation not including the wire diameter of a metal filament 1. The patterning amount (h) of the metal filament 1 is measured by projecting an image of the patterned metal filament 1 on a screen or the like using a projector.
In the elastomer-metal cord composition of the present invention, it is preferred that a phase difference between the adjacent metal filaments be π/4 to 7π/4. In the elastomer-metal cord composite of the present invention, it is also preferred that the adjacent metal filaments have an elastomer coating ratio of 10% or higher per unit length on a widthwise side surface of the metal cord. Further, in the elastomer-metal cord composite of the present invention, it is preferred that the metal filaments have a patterning amount of 0.03 to 0.30 mm and a patterning pitch of 2 to 10 mm. It is noted here that, in the elastomer-metal cord composite of the present invention, the "straight metal filament" refers to a metal filament that is not intentionally patterned and is thus in a substantially unpatterned state.
The term "elastomer coating ratio" used herein refers to, for example, when a rubber is used as the elastomer, a value calculated based on the following equation after coating the elastomer-metal cord composite of the present invention with the rubber, pulling out a steel cord from the resulting rubber-steel cord composite, and then measuring the length of a rubber-coated part of the steel cord: $Elastomer coating ratio = (Rubber-coated length / Sample length) \times 100 (%)$
The elastomer coating ratio can be calculated in the same manner also when an elastomer other than a rubber is used as the elastomer.
A tire of the present invention is characterized by including the elastomer-metal cord composite of the present invention.

EFFECTS OF THE INVENTION

According to the present invention, an elastomer-metal cord composite capable of improving the performance of a tire, in which composite a metal cord composed of a bundle of metal filaments that are parallelly aligned without being twisted together is coated with an elastomer, and a tire including the same can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a drawing of a metal filament that describes the definitions of a patterning amount (h) and a patterning pitch (p) of the metal filament.
[FIG. 2] FIG. 2 is a widthwise partial cross-sectional view illustrating an elastomer-metal cord composite according to one preferred embodiment of the present invention.
[FIG. 3] FIG. 3 is a schematic plan view illustrating a metal cord of the elastomer-metal cord composite according to one preferred embodiment of the present invention.
[FIG. 4] FIG. 4 is a schematic widthwise cross-sectional view illustrating the metal cord of the elastomer-metal cord composite according to one preferred embodiment of the present invention.
[FIG. 5] FIG. 5 is a schematic widthwise cross-sectional view illustrating a metal cord of an elastomer-metal cord composite according to another preferred embodiment of the present invention.
[FIG. 6] FIG. 6 is a schematic widthwise cross-sectional view illustrating a metal cord of an elastomer-metal cord composite according to yet another preferred embodiment of the present invention.
[FIG. 7] FIG. 7 is a schematic half cross-sectional view illustrating a tire according to one preferred embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

The elastomer-metal cord composite of the present invention will now be described in detail referring to the drawings. FIG. 2 is a widthwise partial cross-sectional view illustrating an elastomer-metal cord composite according to one preferred embodiment of the present invention; FIG. 3 is a schematic plan view illustrating a metal cord of the elastomer-metal cord composite according to one preferred embodiment of the present invention; FIG. 4 is a schematic widthwise cross-sectional view illustrating the metal cord of the elastomer-metal cord composite according to one preferred embodiment of the present invention. An elastomer-metal cord composite 10 of the present invention is obtained by coating, with an elastomer 3, a metal cord 2 composed of a bundle of two to ten metal filaments 1 that are parallelly aligned in a single row without being twisted together. In the illustrated example, five metal filaments 1 are parallelly aligned without being twisted together, forming the metal cord 2.
In the metal cord 2 according to the elastomer-metal cord composite 10 of the present invention, all of the metal filaments 1 are patterned in the same patterning amount at the same pitch, and the metal cord 2 includes at least one pair of metal filaments arranged in such a manner that the adjacent metal filaments have different phases from each other. In this manner, in the elastomer-metal cord composite 10 of the present invention, by allowing the metal filaments 1 having the same patterning amount and the same patterning pitch to be in different phases, such metal filaments 1 are prevented from having the same phase. By adopting this constitution, an elastomer is allowed to sufficiently infiltrate between adjacent metal filaments 1, as a result of which the steel cord can undergo in-plane deformation when a compressive input is applied thereto, and deterioration of the fatigue characteristics of the steel cord can thereby be inhibited.
In addition, as described above, in a bundle of metal filaments, an elastomer hardly infiltrates between adjacent filaments, and this causes the generation of a non-elastomer-coated region where filaments are not coated with the elastomer. Accordingly, when a metal cord obtained by bundling metal filaments without twisting them together is used as a cord of a belt, the metal filaments in such a non-elastomer-coated region are displaced from each other during tire rolling, as a result of which the in-plane rigidity of the belt is reduced, and the steering stability may consequently be impaired. However, in the elastomer-metal cord composite 10 of the present invention, since the elastomer 3 sufficiently infiltrates between adjacent metal filaments 1, the above-described defects can be eliminated and, by using the elastomer-metal cord composite 10 of the present invention as a cord of a belt, the in-plane rigidity of the belt can be enhanced and the steering stability can be improved. In order to favorably attain this effect, adjacent metal filaments 1 have an elastomer coating ratio per unit length of preferably 10% or higher, more preferably 20% or higher, on a widthwise side surface of the metal cord 2. The adjacent metal filaments 1 are coated at a ratio of still more preferably 50% or higher, yet still more preferably 80% or higher, most preferably 90% or higher.
In the elastomer-metal cord composite of the present invention, the phase is different between adjacent metal filaments at least one spot in the metal cord 2, and the phase difference is preferably π/4 to 7π/4. By controlling the phase difference in this range, the effects of the present invention can be favorably attained. The phase difference is more preferably π/2 to 3π/2, particularly preferably π.
In the elastomer-metal cord composite 10 of the present invention, an excessively large patterning amount of the metal filaments 1 makes a distance (w) between the metal cords 2 in the elastomer-metal cord composite 10 short, and this causes a reduction in the belt strength when the elastomer-metal cord composite 10 of the present invention is used as a belt. Accordingly, the patterning amount of the metal filaments 1 is preferably 0.03 to about 0.30 mm. When the patterning amount is greater than 0.30 mm, since the strength of the elastomer-metal cord composite is reduced, the effects of the present invention cannot be sufficiently attained. Particularly, from the standpoints of the distance (w) between the metal cords 2 and the strength of the metal filaments 1, when the metal filaments 1 are patterned, the patterning amount is preferably 0.03 to 0.30 mm, more preferably 0.03 to 0.25 mm, most preferably 0.03 to 0.20 mm. Further, the patterning pitch of the metal filaments 1 is preferably 2 to 30 mm, more preferably 2 to 20 mm, most preferably 3 to 15 mm.
In the metal cord 2 illustrated in FIGs. 3 and 4, the patterned metal filaments 1 are patterned in the width direction of the metal cord 2; however, in the elastomer-metal cord composite 10 of the present invention, the patterning direction of the metal filaments 1 may be tilted with respect to the width direction of the metal cord 2. FIG. 5 is a schematic widthwise cross-sectional view illustrating a metal cord of an elastomer-metal cord composite according to another preferred embodiment of the present invention. Even in this structure, a rubber can sufficiently infiltrates between adjacent metal filaments 1, so that the effects of the invention can be attained. Nevertheless, in the elastomer-metal cord composite 10 of the present invention, from the standpoint of lightweightness, it is more preferred that the patterning direction of adjacent metal filaments 1 be the width direction of the metal cord 2, since this can reduce the thickness of the elastomer-metal cord composite.
Further, in the elastomer-metal cord composite of the present invention, the patterning is not limited to two-dimensional patterning, and may be three-dimensional patterning. FIG. 6 is a schematic widthwise cross-sectional view illustrating a metal cord of an elastomer-metal cord composite according to yet another preferred embodiment of the present invention. In the illustrated example, each metal filament 1 is helically patterned, and five helically-patterned metal filaments 1 are parallelly aligned in a single row without being twisted together, forming the metal cord 2.
In the elastomer-metal cord composite 10 of the present invention, the "metal filament 1" generally refers to a wire-like metal that contains steel, namely iron, as a main component (the mass of iron exceeds 50% by mass with respect to a total mass of the metal filament), and may be made of iron alone, or may contain a metal other than iron, such as zinc, copper, aluminum, or tin.
In the elastomer-metal cord composite 10 of the present invention, the surface of the metal filament 1 may be treated by plating. The type of the plating is not particularly restricted, and examples thereof include zinc plating, copper plating, brass plating, and bronze plating. Thereamong, brass plating is preferred since a brass-plated metal filament exhibits excellent adhesion with rubber. In the brass plating, the ratio of copper and zinc (copper: zinc) is usually 60:40 to 70:30 based on mass. The thickness of the resulting plated layer is generally 100 nm to 300 nm.
In the elastomer-metal cord composite 10 of the present invention, the wire diameter, the tensile strength and the cross-sectional shape of the metal filament 1 are not particularly restricted. For example, the metal filament 1 may have a wire diameter of 0.15 mm to 0.40 mm. As the metal filament 1, a metal filament having a tensile strength of 2,500 MPa or higher can be used. Further, the widthwise cross-sectional shape of the metal filament 1 is also not particularly restricted and may be, for example, elliptical, rectangular, triangular or polygonal; however, it is preferably circular. In the elastomer-metal cord composite 10 of the present invention, a wrapping filament may be used as well when it is necessary to restrain the metal filaments 1 constituting the metal cord 2.
Moreover, in the elastomer-metal cord composite 10 of the present invention, the elastomer 3 coating the metal cord 2 is also not particularly restricted and, for example, any rubber that is conventionally used for coating a metal cord can be employed. In addition, examples of an elastomer that can be preferably used include diene-based rubbers and hydrogenation products thereof, such as natural rubbers (NR), isoprene rubbers (IR), epoxidized natural rubbers, styrene-butadiene rubbers (SBR), butadiene rubbers (BR, high-cis BR and low-cis BR), nitrile rubbers (NBR), hydrogenated NBRs, and hydrogenated SBRs; olefin-based rubbers, such as ethylene-propylene rubbers (EPDM and EPM), maleic acid-modified ethylene-propylene rubbers (M-EPM), butyl rubbers (IIR), copolymers of isobutylene and an aromatic vinyl or diene monomer, acrylic rubbers (ACM), and ionomers; halogen-containing rubbers, such as Br-IIR, Cl-IIR, brominated isobutylene-p-methylstyrene copolymers (Br-IPMS), chloroprene rubbers (CR), hydrin rubbers (CHR), chlorosulfonated polyethylene rubbers (CSM), chlorinated polyethylene rubbers (CM), and maleic acid-modified chlorinated polyethylene rubbers (M-CM); silicone rubbers, such as methyl vinyl silicone rubber, dimethyl silicone rubber, and methylphenyl vinyl silicone rubber; sulfur-containing rubbers, such as polysulfide rubbers; fluororubbers, such as vinylidene fluoride-based rubbers, fluorine-containing vinyl ether-based rubbers, tetrafluoroethylene-propylene-based rubbers, fluorine-containing silicone-based rubbers, and fluorine-containing phosphazene-based rubbers; and thermoplastic elastomers, such as styrene-based elastomers, olefin-based elastomers, ester-based elastomers, urethane-based elastomers, and polyamide-based elastomers. These elastomers may be used individually, or two or more thereof may be used in combination. Further, in these elastomers, an age inhibitor, zinc oxide, stearic acid and the like that are usually used in rubber products such as tires and conveyor bels may be incorporated as appropriate, in addition to sulfur, a vulcanization accelerator and carbon black.
The elastomer-metal cord composite of the present invention can be produced by any known method. For example, the elastomer-metal cord composite of the present invention can be produced by parallelly arranging the metal cords according to the present invention at prescribed intervals and subsequently coating the thus arranged metal cords from both above and below with an about 0.5-mm thick sheet made of an elastomer. Further, patterning of the metal filaments can be performed by any conventional method using an ordinary patterning machine.
The tire of the present invention will now be described.
A tire 100 of the present invention includes the elastomer-metal cord composite 10 of the present invention, and examples of the tire 100 include tires for passenger vehicles and tires for trucks and buses. FIG. 7 is a schematic half cross-sectional view illustrating a tire according to one preferred embodiment of the present invention. The illustrated pneumatic tire 100 includes: a tread portion 101 which forms a ground-contact part; a pair of side wall portions 102 which continuously extend inward in the tire radial direction on the respective sides of the tread portion 101; and bead portions 103 which continuously extend on the inner circumferential side of each side wall portion 102.
In the illustrated tire 100, the tread portion 101, the side wall portions 102 and the bead portions 103 are reinforced with a carcass 104, which is composed of a pair of carcass layers toroidally extending from one bead portion 103 to the other bead portion 103. In addition, the tread portion 101 is reinforced with a belt 105, which is composed of at least two layers (a first belt layer 105a and a second belt layer 105b in the illustrated example) that are arranged on the tire radial-direction outer side of the carcass 104 in a crown region. It is noted here that the carcass 104 may be composed of plural carcass layers, and an organic fiber cord extending in a direction substantially perpendicular to the tire circumferential direction, for example, at an angle of 70° to 90°, can be suitably used.
In the tire 100 of the present invention, the above-described elastomer-metal cord composite 10 of the present invention can be used in the first belt layer 105a and the second belt layer 105b. By using the elastomer-metal cord composite 10 of the present invention, the thickness of the steel cord of the first belt layer 105a and that of the second belt layer 105b can be reduced, so that the weight of the tire can be reduced. Moreover, by using the elastomer-metal cord composite 10 of the present invention as a cord of the belt, the durability of the belt and the steering stability can both be improved at the same time.
The tire 100 of the present invention may have any constitution as long as it includes the elastomer-metal cord composite 10 of the present invention, and other aspects of a specific tire structure are not particularly restricted. In addition, the part to which the elastomer-metal cord composite 10 of the present invention is applied is not restricted to the belt 105. For example, the elastomer-metal cord composite 10 of the present invention may be used as a belt reinforcing layer arranged on the tire radial-direction outer side of the belt 105, or as other reinforcing member. As a gas filled into the tire 100, an air having normal or adjusted oxygen partial pressure, as well as an inert gas such as nitrogen, argon or helium, can be used.
The present invention will now be described in more detail by way of Examples thereof.

Steel cords illustrated in FIG. 3 were produced by bundling five steel filaments (wire diameter: 0.25 mm). The patterning amount and the patterning pitch were as shown in Table 1. The thus obtained steel cords were each coated from both above and below with an about 0.5-mm thick sheet made of a rubber, and the resultants were vulcanized at 160°C for 20 minutes. As the rubber, the following one was used.

Natural rubber	100 parts by mass
Carbon black ^*1	61 parts by mass
Zinc white	5 parts by mass
Age inhibitor
^*2	1 part by mass
Vulcanization accelerator
^*3	1 part by mass
Sulfur	5 parts by mass

*¹ N326, DBP oil absorption amount: 72 ml/100 g, N₂SA: 78 m²/g
*² N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine (trade name: NOCRAC 6C, manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)
^*3 N,N'-dicyclohexyl-2-benzothiazyl sulfenamide (trade name: NOCCELER DZ, manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)

A rubber-steel cord composite was produced in the same manner as in Example 1, except that all of the steel filaments were straight.

A rubber-steel cord composite was produced in the same manner as in Example 1, except that no phase difference was formed.
Using each of the thus obtained rubber-steel cord composites as a belt layer-reinforcing material, a tire of the type illustrated in FIG. 6 (size: 205/55R16) was produced. The end count of the steel cords in each rubber-steel cord composite was set at 25 cords/50 mm, and the belt angle was set at 62°. For the thus obtained tire, the steel cord breaking property and the steering stability were evaluated by the below-described procedures. The elastomer coating ratio was also determined by the below-described procedure. The results thereof are in Table 1.

The elastomer coating ratio was determined by pulling out each rubber-steel cord composite from the respective tires at four spots distributed over the entire belt width on the tire circumference and measuring the amount of the rubber remaining on the cord. The elastomer coating ratio was calculated using the following equation: $Elastomer coating ratio = (Rubber-coated length / Sample length) \times 100 (%)$
It is noted here that the rubber-coated length is the length of a region of the steel cord surface that was completely covered with the rubber when the steel cord was observed from a direction perpendicular to the cord longitudinal direction. A larger value indicates a higher adhesive strength and superior performance.

From each of the thus obtained rubber-steel cord composites, a bundled cord composed of a prescribed number of steel filaments was collected, and this bundled cord was dissected and held with a gap of about 100 mm. The bundled cord was slowly stretched until it was broken, and the breaking load was measured using a universal material tester manufactured by Instron Corporation. The thus obtained value was indicated as an index, taking the value of Comparative Example 1 as 100. A larger value means superior strength. The thus obtained results are shown in Table 1.

Each test tire was mounted on a standard rim prescribed in the JATMA Standard and subsequently inflated to an internal pressure of 100 kPa under a load of 1.05 times of normal load. A vehicle equipped with an autopilot system capable of performing 8-shaped turning was driven with the tire on an 8-shaped turning test course for a total of 300 laps at a turning acceleration of 0.7 G and a speed of 25 km/h, after which the tire was dissected and the belt breaking property was compared. In Examples, the incidence of steel cord breakage was converted into an index, taking Comparative Example 1 as a reference. An evaluation of "⊚" (good) was given when the index value was less than 100; an evaluation of "○" (equivalent) was given when the index value was 100 or greater but less than 110; or an evaluation of "×" (poor) was given when the index value was 110 or greater. The results thereof are shown in Table 1. A smaller value means superior cord fatigue characteristics.

After each test tire was mounted on a standard rim prescribed in the JATMA standard, the steering stability was evaluated by a driving test based on the driver's feel on a dry circuit. In Examples, poor steering stability was evaluated as "×" and excellent steering stability was evaluated as "⊚", giving an evaluation of "○" to Comparative Example 1 as a reference, and the results thereof are shown in Table 1.

[Table 1]

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Comp. Example 1	Comp. Example 2
Number of bundles	5	5	5	5	5	5	5	5
Patterning shape	2D	2D	2D	2D	2D	2D	straight	2D
Patterning amount (mm)	0.05	0.15	0.15	0.2	0.15	0.35	-	0.15
Patterning pitch (mm)	5	5	5	5	10	5	-	5
Phase difference	π	π	π/2	π	π/2	π	-	0
Elastomer coating ratio (%)	82	90	85	95	85	99	0	0
Strength (index)	98	95	94	93	96	80	100	95
Steel cord breaking property	⊚	⊚	⊚	⊚	⊚	⊚	×	×
Steering stability	⊚	⊚	⊚	⊚	⊚	⊚	○	○

From the above, it is seen that the elastomer-metal cord composite of the present invention has an excellent elastomer coating ratio.

DESCRIPTION OF SYMBOLS

1: metal filament
2: metal cord
3: elastomer
10: elastomer-metal cord composite
100: tire (pneumatic tire)
101: tread portion
102: side wall portion
103: bead portion
104: carcass
105: belt layer

Claims

An elastomer-metal cord composite obtained by coating, with an elastomer, a metal cord composed of a bundle of two to ten metal filaments that are parallelly aligned in a single row without being twisted together,
wherein
the metal filaments are patterned in the same patterning amount at the same pitch, and
the metal cord comprises at least one pair of adjacent metal filaments having different phases from each other.
The elastomer-metal cord composite according to claim 1, wherein a phase difference between the adjacent metal filaments is π/4 to 7π/4.
The elastomer-metal cord composite according to claim 1 or 2, wherein the adjacent metal filaments have an elastomer coating ratio of 10% or higher per unit length on a widthwise side surface of the metal cord.
The elastomer-metal cord composite according to any one of claims 1 to 3, wherein the metal filaments have a patterning amount of 0.03 to 0.30 mm and a patterning pitch of 2 to 10 mm.
A tire comprising the elastomer-metal cord composite according to any one of claims 1 to 4.